A milling cutter of the above mentioned kind has become known from a model of the Eri Company. The purpose of such a milling cutter is the machining of plane surfaces of large diameter at the front and the back of through holes.
The known milling cutter consists of a shank, at whose face is disposed a radial seating slot in which a cutting part pivotable in a radial direction is inserted. When the milling cutter is driven in rotation, the cutting part can be flipped out of the seating slot in one rotary direction so that it will mill the desired plane surface, while in the other rotary direction the cutting part flips back into the seating slot and can travel through the through hole without machining a milled surface.
It is assumed in the known tool that the recess in the tool body intended for the cutting part to flip into is always free of chips so as to assure that the cutting part will flip in at all. This makes the applicability of the tool to CNC machines questionable because the flipping in and out of the cutting part does not always succeed.
Furthermore, great precision cannot always be achieved because, on the one hand, the cutting part must be rotatably mounted and, on the other hand, it is subjected to great pressure when milling in reverse.
SUMMARY OF THE INVENTION
It is an object of the invention to further develop a milling cutter of the above mentioned kind so that it will function safely operationally and have a longer life at lower costs.
The problem posed is solved in that two cutting part are mounted so as to be radially movable and lockable in seating slots of the tool head, opposing each other and contacting each other in the area of the seating slot. The shifting motion of the cutting parts is accomplished by a rocker which is mounted so as to be rotatable about the longitudinal axis of the tool and whose steering bolts, attached to its face and pointing in an axial direction, engage coordinated recesses in the cutting parts.
The arrangement of two cutting parts pointing radially outward results in the significant advantage that the cutting parts support each other in their center area, thus absorbing the machining pressure relatively well. Another significant advantage is that the steering bolts which move the cutting parts in and out are themselves not affected by the machining pressure, remaining completely free of the machining pressure and, therefore, not being subject to wear. Rather, the cutting parts support each other in their center area on the one hand, while their outer area is in contact with strike surfaces of the seating slot in the tool body on the other hand.
The radial shifting of the cutting parts is accomplished by a cylindrical shaft, called a rocker, at one face of which the steering bolts are disposed, the rocker being rotatably mounted in the bore of a guide sleeve fixed to the housing and driven in rotary motion by the tool shank.
Accordingly, when the rocker turns due to the rotation of the shank, the steering bolts will perform a slider crank motion (eccentric), causing the cutting parts to be either moved radially out of the seating slot in the tool head, machining the desired milled surface at the front or back of the through hole, or, if the shank is driven in the other rotary direction, the steering bolts move the cutting part radially in so that the tool can travel through the through hole.
The shank is rotatably mounted in roller thrust bearings in the tool jacket fixed to the housing and can pivot in the jacket only within limits by a defined pivot angle.
The pivot angle of the shaft in the jacket is limited in that there is rigidly fastened to the jacket bore a twist stop designed as a circular segment whose faces have strike surfaces which a key disposed in a radial slot in the shank can be caused to contact. Consequently, upon the key striking one of the strike surfaces of the twist stop, the cutting parts are pushed radially out of their seating slot in the tool body and perform the milling operation, whereas upon the key striking the opposite strike surface of the twist stop, the cutting parts will disappear in the seating slot of the tool head, and the tool head can travel through the through hole.
In order to be able to perform milling operations of different diameters quickly it is preferable to detain the guide sleeve together with the rocker and the cutting parts in the tool body, so as to be readily exchangeable. This is accomplished by the guide sleeve being joined to the tool jacket by means of screws, and by the rocker being detachably joined to the shank in the manner of a plug-in coupling so that, while being able to be pulled out in and axial direction, it is coupled to the shank in a radial direction.
To mill different diameters, the guide sleeve is then simply unscrewed from the jacket and can be pulled off the tool together with the rocker, thereby disengaging the plug-in coupling between the rocker and the shank. Then another guide sleeve, such as one of larger diameter with different cutting parts, is installed and the rocker joined to the shank via the plug-in coupling, and the guide sleeve is screwed to the jacket so that, after this simple replacement, milling operations of larger diameters can now be performed.
Another embodiment of a milling cutter according to the present invention provides for the shank to be mounted in the milling cutter jacket in ball bearings (as in the embodiment described first), but that the shank has a radial shoulder of larger diameter, against which the ball bearings rest in front and back in longitudinal direction, making this arrangement capable of transmitting greater axial forces from the rotating shank to the milling tool jacket.
This embodiment is further characterized in that a twist brake (brake device) is provided to assure between the retraction and extension of the cutters a braked intermediate position so that, for instance, when retracting the cutters, they will not bounce back from their retracted position and unintentionally project out of the tool head, which would lead to an incorrect machining operation.
Conversely, the twist brake ensures that, when the cutters are in their fully extended position in the tool head, they are not unintentionally retracted into the cutter head again due to the shank twisting too quickly with respect to the milling tool jacket, thereby initiating an incorrect milling operation. The spring-back of the shank with respect to the milling cutter jacket is effected by a key connected to the shank striking coordinated strike surfaces of a segment shaped twist stop which is connected to a milling cutter jacket. When reversing the direction of rotation of the shank, i.e. between retraction and extension of the cutters (i.e. between the key contacting the one or the other strike surface of the twist stop), the twist brake interposes a braked intermediate position so that the cutters are prevented from inpacting too severly and abruptly and, associated therewith, from being unintentionally shifted in the cutter head of the milling cutter.
Other features of the invention are the subject of the dependent claims.
The subject of the present invention follows not only from the subject of the individual patent claims, but also from the combination of various patent claims.
All data and features disclosed in the documents, in particular the physical designs illustrated in the drawing are claimed as being essential to the invention to the extent they are novel, singly or in combination, versus the state of the art.
The invention is explained below in greater detail by reference to drawings showing but one embodiment. Further features and advantages of the invention are evident from the drawings and their description.